1. Field of the Invention
This invention relates to a printed circuit board and more particularly to a double-face flexible printed circuit board for use in a compact apparatus such as a camera or the like having an extremely limited space for arranging electrical circuit elements.
2. Description of the Prior Art
It has recently become general practice to have electrical circuit elements densely arranged within precision apparatus or equipment such as cameras or the like. The electrical circuit arrangement has tended to increase in scale and complexity. Meanwhile, these types of apparatus tend to have more compact bodies and more complex and diversified devices packed within their compact bodies. This tendency often results in an extremely limited space for electrical circuit elements. To cope with this, it is common practice to have the majority of electrical circuit elements integrated or assembled on a flexible printed circuit board and to place the assembled flexible board in a narrow clearance that remains between an internal mechanism and covering of the apparatus. This takes advantage of the flexibility of the printed circuit board.
The electrical circuit elements generally include some type of control circuit elements such as a central processing unit (hereinafter referred to as CPU) for the purpose of electrically controlling various devices included in the apparatus. It is considered necessary to perform an electrical check on these elements after they are soldered to the printed circuit board or to mount an electrical element for adjusting the value of input information. Generally, for the electrical check of a CPU mounted on a flexible circuit board, a lead frame wiring pattern is arranged on the circuit board and the electrical check is accomplished by bringing a probe pin into contact with the wiring pattern. However, the flexible printed circuit board is not as strong as it is flexible. Therefore, direct probing might break or damage the wiring pattern or the circuit board disposed in the clearance between internal mechanisms. To prevent this, various solutions have been employed. One solution involves reinforcing the circuit board by attaching a hard lining plate made, for example, of glass-epoxy resin or paper-phenol resin, to the reverse side of the pattern where the probing pin comes into contact. Another solution involves arranging the checking pattern in a roundabout way to touch the flat surface of a member of the apparatus such as a casing or base plate.
However, the method of attaching the reinforcement lining plate to the flexible circuit board increases the number of parts as well as the number of manufacturing processes and thus results in an increase in cost. Further, the other roundabout arrangement to extend the checking pattern to a flat surface member decreases the available area for the arrangement of parts. This method not only prevents the desired dense arrangement of the parts but also results in an increased size for the flexible circuit board.
This will be more clearly understood from the following description with reference to FIGS. 5 and 6 of the accompanying drawings. FIG. 5 shows in a sectional view an example of the conventional printed circuit board mounting arrangement within a single-lens reflex camera. FIG. 6 is a development view of the printed circuit board. Reference numeral 1 denotes a double-face flexible printed circuit board; numeral 2 denotes a CPU provided with a control circuit constructed of a molded electrical circuit element of the known flat package type. CPU 2 is arranged to perform varied kinds of functions. Electrical check patterns 3 and 3' are drawn from the lead frame of the CPU 2 and are arranged to permit an electrical check after the CPU 2 is mounted on the flexible printed circuit board 1. The electrical check patterns 3 and 3' include patterns 3a-3h respectively electrically connected to the lead frames 2a-2h of the CPU 2. The flexible printed circuit board 1 is provided with a reinforcement lining plate 4. Further, the double-face flexible printed circuit board 1 is secured to a camera body 5 by a screw 7 through a mounting screw hole 6. A substrate 8 is arranged for receiving film sensitivity information and is connected by soldering via holes 9 to the double-face flexible board 1. The substrate 8 is mounted on a base plate 10 arranged to carry a film rewinding fork. The camera is provided with an upper cover 11 and a pentagonal roof type prism 12. In carrying out an electrical check on the CPU 2 after mounting it on the flexible board 1, a probing pin 13 is brought into electrical contact with the electrical check patterns 3 and 3' arranged from the lead frames 2a-2h on the flexible board 1. The electrical check is performed as a final check for the camera before the upper cover is mounted.
In a compact precision apparatus like a camera, however, a flexible printed circuit board is generally disposed within a clearance between an internal mechanism and a covering of the apparatus, such as a clearance which remains between the upper cover 11 and the pentagonal prism 12. Such being the location of the flexible board 1, the flexible board 1 tends to become damaged or broken by the probing pin 13 when the pin 13 is brought into contact with the electrical check patterns.
To prevent such damage, a hard lining plate 4 made of glass-epoxy resin or paper-phenol resin is applied to one side of the flexible board opposite to the side on which the electrical check patterns are arranged, as shown in FIG. 5. In another solution the above-stated problem, wiring for the electrical check patterns 3, is extended to a flat surface of a member disposed within the camera body 5. The conventional arrangement applying the reinforcement plate 4 to the flexible printed circuit board 1 results in an increased cost as it necessitates an additional manufacturing process. An arrangement to extend the wiring of the electrical check patterns 3 to an area such as that indicated by the numeral 14 in FIG. 6 also results in an increased cost because it increases the size of the flexible board 1 and substantially decreases the density of the circuit arrangement.
In a camera provided with an electronic circuit arrangement for controlling various devices, the elements which supply input information to a control circuit include electrical circuit adjustment elements such as selective resistors to be used by selecting the resistance values thereof after the optimum resistance value for the circuit has been measured. These adjustment elements and fixed electrical circuit elements which have preset electrical values and require no adjustment, such as fixed resistors, fixed capacitors, semiconductor elements, etc., are densely mixed on a narrow printed circuit board. Therefore, in carrying out adjustment work on an assembly line, work efficiency has been low as one element tends to be mistaken for another. Further, this has necessitated some additional processes such as an arrangment to attach identification marks to the elements to be adjusted.